I am unclear on any particular problem you are reporting, other than some apparently random changes to threading. That, I believe, may have been a problem once, but should not now be happening. The threading status for a folder is stored locally in the msf file for the folder. If you do a folder repair, that would reset it. With the release of version 136, setting thread status for multiple folders can now be one in settings>appearance. For ver 128, it' possible to set one folder and, with a few clicks, include the same setting for all folders within one account. My perception is that the feature now in 136 will soon appear in the ESR release, which is now 128.

Thanks for your reply.

I agree: it "should not now be happening." But it is. It happened yesterday, to one of my inboxes, after I had re-set it earlier in the day.

I'm pretty sure I've never done a folder repair on any of the commonly used folders (inbox, sent, etc.) I'm certain I haven't done one recently, but the problem has become more common recently, which is what prompted me to write in the first place.

I'm using version 128, which settings says is current, not ESR 136. There is no "appearances" under settings; there is a "Language and Appearance" setting but nothing about folders there.

So your suggestions aren't helping. The problem persists. As I said above: Not the end of the world, but aggravating.

Are you using Table View or Cards View? If you are using Table View, does "Thread" column header appear in the column header? (Please see the attached image.)

If "Thread" column header appears in the column header, clicking it will toggle message threads. Maybe you accidentally clicked it so that unthreaded message list became threaded message list.

Here is my own documentation on threading, duplicating the above, but it may help: You need to highlight each folder and click View>sort by>unthreaded. If this applies to just a few folders, just repeat the process as necessary. If you have many folders or plan to add many new folders, you may wish a different approach, below:

FOR NEW FOLDERS To change default for *new* folders, In config editor, you can change default that applies to NEW folders you set up: mailnews.default_view_flags 0 =unthreaded

Config editor is available at Tools>settings>general and scroll to bottom right.

 ------------

FOR EXISTING FOLDERS These steps may help: To set many *existing* folders, follow these steps: This must be done on an account by account basis.

1. select table view - the icon just to right of 'quick filter' button above message list pane
2. select a message folder and apply all desired attributes - View>sort by from menu bar (if not shown, click alt key)
3. click the icon at right side of column display in message list pane
4. select the entry near bottom 'Apply current view to...'
5. highlight 'folder and children'
6. move mouse left to see account name and move left again to display all account folders. Now CLICK. a small menu will appear to confirm setting all folders within that account.

COMMENT: The setting of settings>appearance should be in the ESR release later this year, and that simplifies/replaces the above.

Thanks for the replies.

I haven't checked all the folders (there are a lot of them) but all those I checked are in card view. That includes the one that reverted to threaded this morning.

The procedure David describes is the one I've been following.

So no dice.

I'm using version 128, which settings says is current, not ESR 136. There is no "appearances" under settings; there is a "Language and Appearance" setting but nothing about folders there. So your suggestions aren't helping. The problem persists. As I said above: Not the end of the world, but aggravating.

Version 128 is the ESR channel. Version 136/137/138 is the "Release" channel, where the new feature David spoke of exists. If you have no add-ons, you can switch to release with instructions at https://blog.thunderbird.net/2025/03/thunderbird-release-channel-update/

If you have add-ons and you wish to switch, please tell us which ones.

Thanks. I prefer not to switch, so I'll just live with the problem unless there's another solution. The problem is now worse than it was: more frequent and impacting inbox, trash, etc. If only this were the worst problem i had to contend with!

It is just a few steps in the ESR. It may look complex, but just takes a few minutes:

This is the official (to my knowledge) documentation. Well worth the read https://support.mozilla.org/en-US/kb/message-threading-thunderbird

Here is my own documentation on threading, duplicating the above, but it may help: You need to highlight each folder and click View>sort by>unthreaded. If this applies to just a few folders, just repeat the process as necessary. If you have many folders or plan to add many new folders, you may wish a different approach, below:

FOR NEW FOLDERS To change default for *new* folders, In config editor, you can change default that applies to NEW folders you set up: mailnews.default_view_flags 0 =unthreaded

Config editor is available at Tools>settings>general and scroll to bottom right.

 ------------

FOR EXISTING FOLDERS These steps may help: To set many *existing* folders, follow these steps: This must be done on an account by account basis.

1. select table view - the icon just to right of 'quick filter' button above message list pane
2. select a message folder and apply all desired attributes - View>sort by from menu bar (if not shown, click alt key)
3. click the icon at right side of column display in message list pane
4. select the entry near bottom 'Apply current view to...'
5. highlight 'folder and children'
6. move mouse left to see account name and move left again to display all account folders. Now CLICK. a small menu will appear to confirm setting all folders within that account.

Thanks for your reply.

When Wayne wrote about the ESR vs standard versions, I went to the link he provided, read it, and opted NOT to switch.

However, the documentation you provided in the link above suggests a config change which I just tried to change the default settings. There's nothing in the folders at present, so I can't test it immediately, but will do so and see if maybe that change solves the problem.

To clarify, the config editor entry does not change existing folders, only folders you create in the future. To change existing folders, you need to do the steps mentioned. Unless you have many addons that may need to be updated, switching to the monthly version may be preferable - unless you prefer the ESR as it is not updated as frequently.

Thanks for your reply.

As I noted in my first posting here, I followed the steps I assume you're referring to (change the sort in each folder from threaded to unthreaded) before writing my first post. The problem is that these same folders keep reverting from unthreaded to threaded seemingly at whim.

As I also noted above, I read the link about the 2 systems and prefer the one I'm using.

Thanks again.